Alcoholism and alcohol-related phenotypes have a strong genetic component. Numerous candidate genes have been hypothesized to be critical in determining these phenotypes including NMDA, serotonin and GABA systems. Typically, the way to demonstrate which of these candidate molecules are in fact responsible for the phenotype is through the use of knock-out mice. In some instances, the ability to address this issue is complicated by the fact that the mutation is embryonic or neonatal lethal making it impossible to ascertain the role of the gene in most behavioral phenotypes, particularly ethanol-related behaviors. One method of eliminating problem is through the use of chimeric mice. Chimeric mice are made by mixing mutant and wild-tax e many instances, the presence of wild-type cells is able to eliminate the lethality allowing for the analysis of animals. NMDA receptors have been hypothesized to mediate multiple alcohol-related effects including increased alcohol consumption and severity of withdrawal effects. Additionally, NMDA receptors have been shown to be important in responses to stress. The NMDA receptor complex is made up of multiple subunits and it is unclear which of the subunits are critical for these effects. Two subunits that have been hypothesized to be important are the NRI and NR2B subunits. Knock-outs of both of these subunits are embryonic lethal and thus, the definitive resolution of the role of each receptor is unknown. To determine the role of these receptors, two different chimeric combinations will be make: NRI-/-<-> wild-type and NR2B-/-<-> wild-type chimeric mice. Adult chimeric mice will be tested on both a two-bottle choice test of ethanol consumption and in a response to stress test using foot shock evaluated in an elevated plus maze. Subsequently, the brains of each chimeric mouse will be analyzed histologically to determine 1) if there is a gene dosage effect i.e. if the behavior is more abnormal in chimeric mice with a higher percentage of mutant cells, and 2) if there is a greater importance of knock-out cells in some brain regions versus others. This data will provide insights into the role of the NR1 and NR2B genes in these phenotypes.